This discussion is getting a bit distracted from the original request. Let's look at it from a higher level.
What is being requested, regardless of if you call it a "map interface" or whatever, is a single way, for sequences and maps... broadly, anything with a __getitem__, to iterate over all values which one might pass to __getitem__, so that one might (among other things) call __setitem__ to mutate the collection. Like, these are common patterns: for i, x in enumerate(l): # do some stuff, sometimes assign l[i] for k, v in d.items(): # do some stuff, sometimes assign d[k] A way to apply that pattern generically to an object which may be either a sequence or a mapping might be nice. Or some other way of doing this operation - maybe a writable iterator like C++ or Java. -- https://mail.python.org/mailman/listinfo/python-list